Highly sensitive electrical switch



F. J. KENLINE Filed April 2'7, 1960 AMPLIFIER HIGHLY SENSITIVEELECTRICAL SWITCH SWITC u March 2, 1965 4 @AJ 441' 2Z1: BY X W IZTOFA/FXS United States Patent 3,172,016 HIGHLY SENSITIVE ELECTRICALSWITCH Frederick J. Kenline, Buffalo, N.Y., assignor, by mesneassignments, to Patterson Industries, Inc., East Liverpool, Ohio, acorporation of Ohio Filed Apr. 27, 1960, Ser. No. 24,933 4 Claims. (Cl.317132) This invention relates to a highly sensitive electrical switchand more particularly to such a switch which is operative at relativelyhigh temperatures, say, in the order of 300 to 400 F.

Electrical switches operable under such temperatures and having a highdegree of sensitivity, such as operating within a fraction of athousandth of an inch, and of such ability as to give many exactrepetitions in operation are not commercially available.

It is the principal object of the present invention to provide anelectrical switch which will operate under the above prescribed hightemperature conditions in response to movement of its probe or actuatingpart which is in order of a fraction of a thousandth of an inch andwhich is stable or free from drift and will give an exact repetition ofits action under conditions of rapid or slow repetitive use.

Another object of the invention is to provide such a switch which isextremely simple and rugged i-n construction, this simplicity, in fact,largely contributing to its high degree of accuracy which is obtained inpart by eliminating the clearances for movable parts contained incommercially available switches.

Another object of the invention is to provide such a highly sensitiveswitch which is easily set to operate within the required range ofmovement and will stand up under conditions of severe and constant usewithout getting out of repair or changing its operating characteristics.

Another object is to provide such a switch which does not require anyunusual or costly materials, the principal parts of the switch beingdesirably fabricated from a suitable plastic sheet and the contactsbeing of brass or any other metal.

Other objects and advantages of the invention will be apparent from thefollowing description and drawings in which:

FIG. 1 is a vertical section taken on line 11, FIG. 2 through a highlysensitive switch embodying the present invention, with a part of thebody broken away.

FIG. 2 is a top plan view thereof.

FIG. 3 is a schematic drawing showing the electronic switching relayused in conjunction with the switch.

An important feature of the present invention is that the operatingparts of the switch are essentially contained within a body part 5having one or more covers 6 made of a plastic which is resistant to heatboth in not being subject to deterioration under high temperature andalso being dimensionally stable under constant application of thesetemperatures. The present switch was particularly designed to operate ina temperature range of 300 to 400 F., although the invention is notlimited to any particular operating temperature range. For operating inthis range the body and covers of the switch can be made of a synthetictar-acid resin or impregnated body a resin satisfactory for this purposebeing commercially known as grade AAA spauldite such synthetic tar andresin can be obtained by the condensation of a tar acid or a mixture oftar acids by dilute mineral acid. The body 5 is shown as being of simplerectangular form and as having a through cavity 8, the opposite sides ofwhich are closed by the two covers 6, which can be secured by cornerscrews 9. Prefer-ably the housing and cover are provided withregistering mounting holes 10 at their opposite ends by means of whichthe switch can be secured in position.

At one end of the cavity 8, the housing 5 is formed to provide a mount11 for a switch arm 12. To this end the mount 11 is formed to provide aV-shaped notch 13 in its top extending transversely of the housing,preferably the full width thereof. This V-shaped notch 13 receives andsupports a downwardly projecting knife edge 14 of the switch arm 12 andwhich knife edge 14 is formed integrally with the switch arm to providewith the notch 13 a knife edge bearing. An important feature of theinvention is that the switch arm is made of a heat resistant plastic soas not to be subject to deterioration or dimensional changes underrelatively high temperatures. As with the body and its covers, asynthetic tar acid resin such as grade AAA spauldite has been found tobe a satisfactory material for this purpose within an operating range offrom 300 to 400 F.

The outboard end of the switch arm 12 has a contact 15 on its underside.This contact can be of brass of any suitable form, but is shown as beingin the form of a vertical screw extending above the top of the switcharm 12 and having a nut 16 at its upper end by means of which a wire 19can connect this contact screw 15 with a binding post in the form of ascrew 20 extending through the top wall of the body 5. This binding postcan have a nut 21 at its lower end by means of which the wire 19 can beconnected, and can have a nut 22 at its upper end by means of whichconnection can be made to a low energy switching unit as hereinafterdescribed.

The movable contact 15 is held in permanent engagement or contact withthe rounding upper head 24 of a fixed contact 25. This is shown as beingin the form of a screw, which can be made of brass, extending throughthe bottom of the body 5 and held by a pair of nuts 26, 27, the lowerone of which can serve to connect the switch with a low energy switchingunit as hereinafter described.

The pressure contact between the contacts 15, 25 can be provided byhelical compression spring 28 operatively interposed between the top ofthe switch arm 12 near its center and the top of the cavity 8. Thishelical compression spring can be held in position by any suitablemeans, such as by the heads of screws 29, 30 in the body and switch arm,respectively. p

The sensitive part of the switch is in the form of a longitudinallyextensible probe, indicated generally at 32, slidingly mounted in thebottom of the body 5 which opposes the movable contact 15. This probeconsists of an internally threaded tubular pin 33 having an enlargedhead 34 within the cavity 8 which is of conical form to provide an apex35 having substantially point contact with the underside of the flathead 36 of a pin 38 fixed in the arm 12 as by a tap fit. This tubularpin 33 is slidingly mounted in a metal bushing 39 and pro vides aslideway for this pin. Screwed into the outer or lower end of thetubular pin 33 is an externally threaded pin 40 which has a lock nut 41tightening against the outer end of the tubular pin 33 so that the pinscan be set in different axial relations to each other and therebyprovide a composite pin or probe which is longitudinally extensible.

The switch is shown as being actuated by a part 42 which can bemaintained at a high temperature and which moves only a fraction of aone thousandth of an inch in opening and closing the switch.

The switch contacts are connected in the low voltage, low amperage endof the low energy switching unit, and the variation in the contactresistance of its contacts 15, 25 varies the drive signal on the lowenergy switching unit corresponding to changes in the pressure betweenthe contacts. The signal is amplified and then employed to actuate arelay which supplies current at standard voltage to the electricalcontrol component being served. This component in turn operates toreturn the part 42 to the desired position.

For this purpose the binding post is shown as connected to one side 45of a low voltage, low amperage line the other side 46 of which isconnected to the input of an amplifier 48. The other input terminal ofthis amplifier 48 is connected by a line 49 to the other binding post ofthe switch. The output of the amplifier 48 is connected by lines 50, 51to the input of a relay 52 and is supplied with available power currentthrough power lines 53 and 54. The output lines 55 and 56 from the relayto connections with the electrical component which the switch isdesigned to serve and which operates to return the part 42 to thedesired level.

In the operation of the switch, the head 34 of the extensible actuatingpin or probe 32, when seated on the bottom of the cavity 8, allowscontacts 15, 25 to be closed. This contract is maintained by the helicalcompression spring 28. Under this condition a corresponding microcurrentat a voltage of, say, six volts, passes through the switch and throughthe input of the amplifier 48. A corresponding amplified current issupplied to the relay 52 and can hold this relay either open or closeddepending upon whether the switch is operated as a normally open or anormally closed switch.

It is assumed that the part 42 which controls the switch rises intemperature to a high value, say 300 to 400 F. and that during this risethe operating characteristics of the switch must remain constant andfree from drift and that at this elevated temperature the parts of theswitch must not be subject to deterioration. For this purpose the body 5and arm 12 of the switch are made of plastic, such as grade AAA spauldite, which is stable dimensionally and against deterioration atthese elevated temperatures. It is also assumed that the switch must beopened and closed with movement of a fraction of a one thousandth of aninch of the part 4-2 and for this purpose the switch arm 12 has a knifeedge bearing connection 13, 14 with the body 5 and also the switchoperates essentially through change in contact resistance between thecontacts 15, 25 rather than through physical separation of the surfaces,only because this change in resistance takes place first.

Thus with the switch operating as above described, when the part 42rises the assumed fraction of a one thousandth of an inch it elevatesthe composite probe 32 which moves upwardly in the slideway provided inthe bearing bushing 39. Its head 34 has substantially point contact 35with the bottom of the enlarged head 36 of the pin 38 carried by thesynthetic plastic switch arm 12 and hence this small movement of thepart 42 elevates the outboard end of this arm 12, this arm fulcru-rningabout its knife bearing 13, 14. V

This slight movement of the outboard end of the synthetic plastic arm 12is sufficient to relieve the contact pressure between the contacts 15,25 and this increases the contact resistance between these contacts.Thus this contact resistance can be increased from, say, zero ohms whileclosed to, say, forty thousand ohms or so, at the time the switchoperates. Accordingly the relay parts are shifted from one position tothe other either cutting off or supplying current to the electricalcomponent to be served, depending upon whether the switch is norm-allyopen or normally closed. This reverses the movement of the part 42thereby to withdraw the composite probe 32 and permit the pressurebetween the contacts 15, 25 to increase to its original value at whichtheir contact resistance is restored to the assumed zero chm-s. Throughthe amplifier 48, this restores the relay 52 to its original conditionfor a repetition of the signal.

As previously indicated the switch of the present invenprimary circuitincluding the input to an amplifier, and a secondary circuit includingthe output of said amplifier and a relay responsive to 'a predeterminedrange of change in value of the characteristics of the current flowingthrough said secondary circuit; the combination therewith of a switchhighly sensitive to a very small relative movement between two parts,comprising a fixed contact connected to one side of said primary circuitand being fast to one of said parts, a movable contact connected to theother side of said primary circuit and being in engagement with saidfixed contact, means biasing said movable contact into contact pressurewith said fixed contact, and means actuated by the other of said partsto actuate said movable contact to vary and at the same time maintaincontact pressure between said contacts thereby to vary the contactresistance to current flowing between these contacts and efiect acorresponding change in value, through said predetermined range, of thecharacteristic of the current flowing through said secondary circuit,

2. In a circuit having a low voltage, low amperage primary circuitincluding the input to Ian amplifier, and a secondary circuit includingthe output of said amplifier and a. relay responsive to a predeterminedrange of change in value of the characteristics of the current flowingthrough said secondary circuit; the combination therewith of a switchhighly sensitive to a very small relative movement between two parts,comprising a fixed contact connected to one side of said primary circuitand being fast to one of said parts, a movable contact connected to theother side of said primary circuit and being in engagement with saidfixed contact, means biasing said movable contact into contact pressurewith said fixed contact, a stop limiting the position of said movablecontact to a maximum contact pressure between said contacts, and meansactuated by the other of parts to actuate said movable contact to varyand at the same time maintain said contact pressure between saidcontacts thereby to vary the contact resistance to current flowingbetween these contacts and effect a corresponding change in the value,through said predetermined range, of the characteristics of the currentflowing through said secondary circuit.

3. In a circuit having a low voltage, low amperage primary circuitincluding the input to an amplifier, and a secondary circuit includingthe output of said amplifier and a relay responsive to a predeterminedrange of change in value of the characteristics of the current flowingthrough said secondary circuit; the combination therewith of a switchadapted-tor use in a high temperature environment and sensitive to avery small relative movement between said parts, comprising a hollowbody part made of a plastic resistive to heat and fixed to one of saidparts, a fulcrum in one end of said body, a switch arm made of a plasticresistive to heat and having a knife edge bearing at one end seated insaid fulcrum and having a movable contact at the outer end of saidswitch arm and connected to one side of said primary circuit, a contactconnected to the other side out said primary circuit and fixed to saidbody in line to be engaged by said movable contact, p g means interposedbetween said body and switch arm and biasing said movable contact tohave contact pressure with said fixed contact, a stop mounted on saidbody and limiting the position of said movable contact to a maximumcontact pressure between said contacts, and means actuated by the otherof said parts to move said stop to actuate said switch arm to vary andat the same time maintain contact pressure between said contacts therebyto vary the Contact resistance to current flowing between these nontaotsand effect a corresponding change in the value, through saidpredetermined range, of the characteristics of the current flowingthrough said secondary circuit.

4. The combination set forth in claim 3 wherein the body and switch mmare made of a plastic which is thermally stable over a wide range oftemperatures.

References Cited in the file of this patent UNITED STATES PATENTSSohaelchlin Dec. 26, 1939 Lamb Feb. 10, 1942 Kelleigh Mar. 4, 1958Saint-Amour Sept. 2, 1958 Altier-i Oot. 21, 1958 Henley Apr. 5, 1960

3. IN A CIRCUIT HAVING A LOW VOLTAGE, LOW AMPERAGE PRIMARY CIRCUITINCLUDING THE INPUT TO AN AMPLIFIER, AND A SECONDARY CIRCUIT INCLUDINGTHE OUTPUT OF SAID AMPLIFIER AND A RELAY RESPONSIVE TO A PREDETERMINEDRANGE OF CHANGE IN VALUE OF THE CHARACTERISTICS OF THE CURRENT FLOWINGTHROUGH SAID SECONDARY CIRCUIT; THE COMBINATION THEREWITH OF A SWITCHADAPTED FOR USE IN A HIGH TEMPERATURE ENVIRONMENT AND SENSITIVE TO AVERY SMALL RELATIVE MOVEMENT BETWEEN SAID PARTS, COMPRISING A HOLLOWBODY PART MADE OF A PLASTIC RESISTIVE TO HEAT AND FIXED TO ONE OF SAIDPARTS, A FULCRUM IN ONE END OF SAID BODY, A SWITCH ARM MADE OF A PLASTICRESISTIVE TO HEAT AND HAVING A KNIGE EDGE BEARING AT ONE END SEATED INSAID FULCRUM AND HAVING A MOVABLE CONTACT AT THE OUTER END OF SAIDSWITCH ARM AND CONNECTED TO ONE SIDE OF SAID PRIMARY CIRCUIT, A CONTACTCONNECTED TO THE OTHER SIDE OF SAID PRIMARY CIRCUIT AND FIXED TO SAIDBODY IN LINE TO BE ENGAGED BY SAID MOVABLE CON-